1. Field of the Invention
This invention relates to thrust bearings for rotary cone rock bits that utilize fluid such as air to cool and clean the bit as it works in a borehole.
More specifically, this invention relates to an intermediate thrust bearings radially disposed between a roller cone and a journal and a means to secure and cool the thrust bearings therebetween. The thrust bearing is primarily designed to take axial out thrusting loads on the cones and journals.
2. Background
There are a number of prior art patents that provide some means between rotating cones and their respective journals to take axially directed out thrust loads against radial journal bearing surfaces.
It is within the state of the art to provide a hard metal bearing surface on radially disposed areas of the journal and the cone by either depositing hard metal material to the end of the journal or within radially disposed bearing surfaces in the cone. The deposited hard metal material is subsequently machined to provide a smooth bearing surface between the journal and the rotary cone.
The problems that emerge utilizing the foregoing techniques are many. For example, when hard metal material is metalurgically deposited within the cone or on the radially disposed bearing surfaces of the journal, the heat generated causes stress risers that can result in cracks, especially in rotating cones. In addition, it is difficult, costly and time-consuming to machine these rough, hard metal depositions surfaces to form good bearing surfaces essential to the proper operation and longevity of the rock bit.
The present invention overcomes this difficulty by providing one or more hard metal, non-rotating thrust bearing inserts, interference fitted within either the cone or the end of the journal bearing or both.
U.S. Pat. No. 3,720,274 teaches the use of an intermediate thrust bearing washer freely disposed between radially aligned bearing surfaces formed between the end of the journal bearing pin and a rotating cutter cone associated therewith. The thrust bearing serves to support thrust loads and to stabilize the cutter cones. The thrust washer is allowed to float between the radially disposed bearing surfaces during operation of the bit in a borehole. A difficulty with this arrangement is that, as the rock bit wears in an operating mode, the thrust washer begins to gall causing the beatings to eventually fail.
U.S. Pat. No. 4,270,812 is assigned to the same assignee as the present invention and incorporated hereby by reference. This patent teaches forming a spindle beating surface extending from a journal bearing of a rotary cone rock bit with a diameter less than that of the mating bearing formed by the cutter cone. A cylindrical tubular sleeve of hard low friction metal has an inner diameter greater than the diameter of the spindle bearing. The sleeve is inserted over the spindle bearing and a disc is placed over the end and inside the tubular sleeve. Solder is flowed between the sleeve and the disc to attach the sleeve and disc to the bearing spindle to create a hard-faced bearing spindle on the end of the journal.
While the sleeved spindle is an improvement over the metallurgical application of hardfacing material to the thrust bearing surfaces, edge loading and high frictional loads is a result due to slight misalignments of the cone with the spindle.
U.S. Pat. No. 5,148,879 also assigned to the same assignee as the present invention and incorporated herein by reference, describes and teaches the use of a spindle cap disposed between a spindle pilot beating extending from the end of a main journal bearing and a cone rotatively secured thereto. The floating spindle cap is formed from a softer metallic material than both the spindle bearing and the cone to accommodate for slight misalignments and edge loading between the journal bearings and the cone while working in a borehole.
While the malleable floating spindle cap performs satisfactorily, it is subject to fairly high wear rates resulting in a somewhat shorter bit life.
The present invention utilizes a pressed in, hard metal carbide thrust button that may be employed in the end of the pilot spindle bearing or in the cone. An oppositely apposed softer metal such as a steel disc is used as a bearing surface for the adjacent bearing surface formed by the carbide thrust button. An air fluid passage is formed adjacent to the base of the carbide button or the steel disc to cool the bearing surfaces formed between the steel disc and the carbide thrust button during operation of the bit in a borehole.